(a) Field of the Invention
The present invention relates to a thin film transistor substrate and a metal wiring method thereof, and more particularly to a thin film transistor substrate having superior adhesion ability and diffusion resistance and a metal wiring method thereof.
(b) Description of the Related Art
A thin film transistor (TFT) is one of the devices widely used as switching devices of TFT liquid crystal displays.
A thin film transistor substrate comprises a scanning signal wiring or gate wiring that transfers scanning signals, a picture signal wiring or data wiring that transfers picture signals, a thin film transistor that connects the gate wiring and the data wiring, a pixel electrode connected to the thin film transistor, a gate insulation film that covers the gate wiring, and a passivation film that protects the thin film transistor and the data wiring. A thin film transistor comprises a semiconductor layer that forms a gate electrode and channels, a source electrode, a drain electrode, a gate insulation film and a passivation layer. A thin film transistor is a switching device that transfers or interrupts picture signals transferred through the data wiring depending on scanning signals transferred by the gate wiring.
In TFT LCDs using the thin film transistor as a switching device, an electric field is applied to the liquid crystal using optical anisotropy and polarization of the liquid crystal. The electric field controls arrangement orientation of the liquid crystal molecules to offer images.
In the active matrix liquid crystal display (AMLCD), which is being actively researched and developed, the pixel electrodes connected with the thin film transistor are arranged in matrix form, so that it can offer large screen size and high resolution, such as SXGA or UXGA.
In order to make such large-area and high-resolution liquid crystal displays as SXGA or UXGA, resistance of gate wiring, data wiring and other wirings should be low. In particular, if the resistance of the gate wiring is high, the image quality worsens because of cross-talks due to signal delay caused by the wiring resistance. Metals that can be used for the wiring and their characteristics are summarized in the following Table 1.
TABLE 1Specific resistanceAdhesionHeatMetal(μΩ · cm)PriceabilityresistanceCu2LowLowHighAu3HighLowHighAl4LowHighLowMo20ModerateHighHighCr50ModerateHighHigh
As seen in Table 1, aluminum has low heat resistance. While copper is satisfactory in cost and heat resistance, it has poor adhesion ability to the substrate. Therefore, many researches are trying to improve the adhesion ability of copper to the substrate.
In this regard, wirings of copper alloys, such as Cu/Ti/Si, Cu/TiN/Si, Cu/Ta/Si and Cu/TaN/Si, are widely used. However, these copper alloy wirings are manufactured through complicated processes. Also, they have weak adhesion of Si and Cu, and the anti-diffusion films are thick. Moreover, the anti-diffusion films react with Cu during heat treatment.
Recently, the copper-silver alloy wirings are widely used. However, silver has weak adhesion ability to the glass substrate or silicon layers. The weak adhesion ability causes problems like the thin film's coming off from the substrate or breaking of the wiring. Also, silver is easily damaged by dry-type etching agents for etching insulation film consisting of silicon nitride, etc.